Write a few docs

src/macros.rs

@@ -0,0 +1,34 @@
+//! Internal macros
+
+macro_rules! opaque_future {
+    ($(#[$m:meta])* pub type $name:ident = $actual:ty;) => {
+        opaque_future! {
+            $(#[$m])*
+            pub type $name<> = $actual;
+        }
+    };
+
+    ($(#[$m:meta])* pub type $name:ident<$($param:ident),*> = $actual:ty;) => {
+        #[pin_project::pin_project]
+        $(#[$m])*
+        pub struct $name<$($param),*>(#[pin] pub(crate) $actual)
+        where;
+
+        impl<$($param),*> std::fmt::Debug for $name<$($param),*> {
+            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                f.debug_tuple(stringify!($name)).field(&format_args!("...")).finish()
+            }
+        }
+
+        impl<$($param),*> std::future::Future for $name<$($param),*>
+        where
+            $actual: std::future::Future,
+        {
+            type Output = <$actual as std::future::Future>::Output;
+            #[inline]
+            fn poll(self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> std::task::Poll<Self::Output> {
+                self.project().0.poll(cx)
+            }
+        }
+    };
+}